1. Field of the Invention
This invention relates to a method of and apparatus for forming an internal spline annular member such as an internal spline ring engageable with a splined shaft and an internal gear used as one of elementary gears of a planetary gear mechanism.
2. Description of Related Art
Typically, splines of an internal spline ring engageable with a splined shaft is cut by use of a spline broach. It is also typical to form an internal spline ring in a form rolling method where an annular member is pressed and deformed between an inner spline forming roller and outer backup rollers. One of such form rolling methods is known from, for example, Japanese Unexamined Patent Publication No. 62-144836. Forming or cutting splines by use of a spline broach is relatively unsuitable for small-sized splines and, in addition, defective in forming splines having high strength. In cases where a spline form roller is used to form splines, an internal spline ring having a small module makes it hard to fill the space of the spline form roller sufficiently with flowing material of the ring member, resulting in imprecise forms of spline.
In cases where forging dies are used to form an internal spline ring in cold working, it is needed to apply surface treatment, such as bond coating or surface lubrication treatment and Ti--CN treatment which are costly, to works and dies. Further, the forging die has only short working life in cold working.